In systems comprising a moving medium, it is desirable to quickly and effectively adjust a control valve in such a way that the moving medium gets a given value, independently of the speed of movement, representing heat per unit of time of the moving medium or any other characteristic. A typical example where there is need for such a device is a system for heating buildings by means of heat radiators from a common feeder conduit. A valve is connected into the common feeder conduit, and this will thereafter, dependent upon the need for the moving medium or the content of heat carried up by said medium, be set into a position corresponding to the circumstances, e.g. dependent upon the outside air temperature, the speed of the wind or other characteristics determining the function of a climatization system.
Hitherto this problem has been solved by a conduit, e.g. a flexible tube, being connected on each side of the restriction, presented by the valve, with the other end of said conduits being connected to each end of a U-shaped tube of barometric type. Then one could read the difference in altitude between the medium columns in the two shanks of said U-tube, and this difference formed a measure for the pressure drop of the moving medium during its movement through the valve. The intention was to guide one to set the valve in the desired position. Such an arrangement, however, has not been satisfactory for several different reasons.
In a system of this kind, it is not desired to know the pressure drop across the valve but rather other parameters, which are in a given relationship to said pressure drop, for instance the speed of movement expressed in liters per minute. One could only get this kind of information after making a comprehensive calculation, which could perhaps take place in a graphical way. Further, the relationship between the pressure drop and the speed of movement is not linear but varies according to a complicated rule, and secondly this relation also has the property of being dependent upon the mechanical dimensions of the system, e.g. the magnitude of the valve, a smaller valve causes a high pressure drop corresponding to a given movement, whereas the same pressure drop in a larger valve corresponds to a much greater movement. In addition, the relation is not only dependent upon each existing valve but will also vary in part with the pump pressure created in the system, and in part with the flow resistance in the earlier or subsequent parts of the conduits.
The consequence has been that adjustment in the above mentioned way, known per se, required a reading of the pressure drop, a subsequent mathematical or graphical counting operation, and thereafter a test adjustment of the valve. Then one must check to see if the valve position which was set is the correct position by a renewed reading of the pressure drop, a re-calculation thereof and so on, until one has by a trial and error operation achieved the correct valve of adjustment.
In practice, it has proved that these operations rather often have to be made by persons who are more or less uneducated, and they thereby have a need for a marking on the wheel of the valve in order to read the different positions. This, in turn, has required that the valve should be adjustable for movement between fully opened and fully closed within a single turn of the wheel. Such a valve has always had bad accuracy in adjusting flow.
The lack of accuracy in the adjustment of such a valve also prevents the possibility of making use of the advantage of shaping the valve body in a given way to cause a linear valve control or any other characteristic desired for one reason or another.
Therefore, it is obvious that all of these disadvantages may be eliminated, if one had available, in connection with the valve to be used for control purposes, an instrument, which would, independently of the magnitude of the valve and independently of the pressure in the existing pump arrangement and also independently of the resistance against movement in the preceding and following parts of the conduit system, indicate the magnitude of a desired parameter, e.g. the speed of movement or the quantity of heat transferred by the controlled medium per unit of time or the like.